Wild Oat (Avena fatua) is a monocot weed in the Poaceae family. In Manitoba this weed first evolved multiple resistance (to 4 herbicide sites of action) in 1997 and infests Wheat. Multiple resistance has evolved to herbicides in the Groups A/1, B/2, N/8, and Z/25. These particular biotypes are known to have resistance to fenoxaprop-P-ethyl, flamprop-methyl, imazamethabenz-methyl, and triallate and they may be cross-resistant to other herbicides in the Groups A/1, B/2, N/8, and Z/25.

The 'Group' letters/numbers that you see throughout this web site refer to the classification of herbicides by their site of action. To see a full list of herbicides and HRAC herbicide classifications click here.

Greenhouse, and Laboratory trials comparing a known susceptible Wild Oat biotype with this Wild Oat biotype have been used to confirm resistance. For further information on the tests conducted please contact the local weed scientists that provided this information.

Genetics

Genetic studies on Group A, B, N, Z/1, 2, 8, 25 resistant Wild Oat have not been reported to the site. There may be a note below or an article discussing the genetics of this biotype in the Fact Sheets and Other Literature

Mechanism of Resistance

The mechanism of resistance for this biotype is either unknown or has not been entered in the database. If you know anything about the mechanism of resistance for this biotype then please update the database.

Relative Fitness

There is no record of differences in fitness or competitiveness of these resistant biotypes when compared to that of normal susceptible biotypes. If you have any information pertaining to the fitness of multiple resistant Wild Oat from Manitoba please update the database.

The Herbicide Resistance Action Committee, The Weed Science Society of America, and weed scientists in Manitoba have been instrumental in providing you this information. Particular thanks is given to Hugh Beckie for providing detailed information.

The aim of the study was to collect seeds of wild oat from the fields where, in spite of the applied herbicides, the weed is very poorly controlled, and to determine under greenhouse conditions if any resistant biotypes are present. In the years 2008-2011, 34 samples of wild oat were collected from fields where the weed was poorly controlled. The biotypes were analyzed in greenhouse experiments to determine if they are resistant to herbicides. Among five resistant biotypes three of them (R3, R4 and R5) were resistant only to iodosulfuron and mesosulfuron, and biotype R2 - only to propoxycarbazone-sodium. Biotype R1 exhibited multiple resistance to iodosulfuron+mesosulfuron and pinoxaden. The use of sulfometuron proves that the mechanism of resistance of two biotypes of wild oat (R1 and R4) to acetolactate synthase inhibitors is associated with target-site mutation. The curve of biotypes R3 and R5 controlled with iodosulfuron+mesosulfuron shows a relatively low resistance index and control of those biotypes with sulfometuron indicates a metabolic resistance..

Two seed samples of Wild Oat (F1, F2) were collected from sugar beet fields in Rhineland-Palatinate in 2011 showing reduced herbicide performance. A seed treatment with gibberellic acid improved uniform germination of the Wild Oat samples during greenhouse experiments. Herbicide action was tested by means of two successive biotests. ACCase-inhibitors (Fenoxaprop, Pinoxaden, Clodinafop+Pinoxaden, Cycloxidim) and one ALS-inhibitor were treated at 2-3-leafstage of the Wild Oat. The visual rating of herbicide efficiency 3 and 4 weeks after treatment showed a cross resistance among the tested ACCase-inhibitors, except for Cycloxidim for both samples. Seed sample F2 revealed an advanced degree of herbicide resistance, declining from Fenoxaprop to Pinoxaden. Herbicide resistance of sample F1 was restricted to single plants. A subsequent genetic analysis of leaf material revealed a target-site mutation I1781L for both samples of Wild Oat. Further investigations are necessary in order to access reduced performance of Iodosulfuron..

Ecological theory predicts that fitness costs of herbicide resistance should lead to the reduced relative abundance of resistant populations upon the cessation of herbicide use. This greenhouse research investigated the potential fitness costs of two multiple herbicide resistant (MHR) wild oat (Avena fatua) populations, an economically important weed that affects cereal and pulse crop production in the Northern Great Plains of North America. We compared the competitive ability of two MHR and two herbicide susceptible (HS) A. fatua populations along a gradient of biotic and abiotic stresses The biotic stress was imposed by three levels of wheat (Triticum aestivum) competition (0, 4, and 8 individuals pot-1) and an abiotic stress by three nitrogen (N) fertilization rates (0, 50 and 100 kg N ha-1). Data were analyzed with linear mixed-effects models and results showed that the biomass of all A. fatua populations decreased with increasing T. aestivum competition at all N rates. Similarly, A. fatua relative growth rate (RGR) decreased with increasing T. aestivum competition at the medium and high N rates but there was no response with 0 N. There were no differences between the levels of biomass or RGR of HS and MHR populations in response to T. aestivum competition. Overall, the results indicate that MHR does not confer growth-related fitness costs in these A. fatua populations, and that their relative abundance will not be diminished with respect to HS populations in the absence of herbicide treatment..

This paper presents the results of surveys conducted on the distribution (regardless of herbicide resistance status) in Australia of wild oats [Avena fatua], fleabane [Erigeron], awnless barnyard grass [Echinochloa colona], annual ryegrass [Lolium multiflorum] and windmill grass [Chloris truncata], and their management. The most widespread resistant species are wild oats and fleabane. Awnless barnyard grass and annual rygrass, both resistant to glyphosate, are found mainly in the north and south of the northern cropping region, respectively. The glyphosate-resistant windmill grass is in the infancy of its spread, mainly confined to the central west plains..

The evolution of weed biotypes resistant to multiple herbicide modes of action, here termed multiple herbicide resistance, is a growing problem around the world. We investigated two multiple herbicide resistant (MHR) wild oat (Avena fatua L.) populations from Montana and hypothesized that they would exhibit fitness costs compared with two herbicide-susceptible (HS) populations. Dose-response tests showed that the MHR populations were resistant to difenzoquat (a membrane disruptor), imazamethabenz (an acetolactate synthase [ALS] inhibitor), flucarbazone (an ALS inhibitor), and tralkoxydim (an acetyl-CoA carboxylase inhibitor). In greenhouse studies, we assessed differences between MHR and HS populations in seed germination, photosynthetic parameters, plant growth, and reproduction. Seeds of one HS population germinated more at cold temperature (4.9°C) and less at high temperature (29.6°C) compared with the other populations. Plants of this HS population also had lower stomatal conductance (23%), intercellular CO2 concentration (7.5%), and transpiration (15.3%) than the other populations, but there were no differences in photosynthetic rates between any populations. Also, there were no differences in relative growth rate among all HS and MHR populations. The MHR populations initiated seed production several days sooner than the HS populations; however, HS populations produced 67% more tillers, and one HS population ultimately produced 43% more seeds than the MHR populations, indicating a potential fitness cost of resistance. With the exception of seed production differences, our results do not indicate a consistent fitness cost. More research is needed in field settings and with resource competition to further evaluate fitness costs in MHR populations..